function sys = notchpeak_sys(domain, fn, bw_f, As)

% init
if strcmp(domain{1}, "s")
    
elseif strcmp(domain{1}, "z")
    Ts = domain{2};
end

s = tf("s");

% design
wn = 2*pi*fn;
bw_w = 2*pi*bw_f;

num_s = s^2 + bw_w*s + wn^2;
den_s = s^2 + 1/As*bw_w*s + wn^2;
sys_s = num_s / den_s;

% output
if strcmp(domain{1}, "s")
    sys = sys_s;
elseif strcmp(domain{1}, "z")
    sys_z = c2d(sys_s, Ts, 'tustin');
    sys = sys_z;
end

end